The present invention relates to the field of active methods and apparatus that use ionizing radiation for the remote interrogation, non-destructive detection, survey, characterization and/or assay of materials that are screened or shielded from the radiation detectors by intervening materials.
Demonstrated techniques for material detection, assay, or lithospheric, chemical and/or isotopic characterizations that use ionizing radiation as the response indicator, and often additionally in a necessary interrogation process, all fundamentally require either a proportional response intensity measurement, or scrutiny of some portion of the energy spectrum for the response emission. The impetus for using ionizing radiation is its ability to penetrate material with modest attenuation of its intensity in optimal configurations, thereby providing an ability to sense or survey the interior of objects by a non-destructive or non-intrusive means. In material detection, assay, or characterization applications involving dense materials (i.e., materials with mass densities greater than liquid water), the effective detection range of radiation providing the response indication is on the order of centimeters to many tens of centimeters, as measured from the interior locations where the radiation is generated to the location that the emission is sensed. The radiation range is primarily a function of the initial energy borne by the emission, with greater energy generally corresponding to greater range. This penetration distance limitation places practical constraints on the ability for remote detection or survey in many applications. Applications where range limitations may be relevant include materials detection in baggage handling and cargo container inspection; coal, ash and slag characterization; structural fitness, process throughput, process holdup and composition uniformity surveys; and lithospheric and diagenic fluid characterization in geologic well and borehole logging applications.
Where penetration distances are short, the most common mitigation involves allowing a longer temporal duration for the measurement of response emissions. Because a diminished fraction of the total emission borne at the point of origin is capable of reaching the detection location with increased penetration distance, a comparatively longer exposure time is required to detect a sufficient number of responses for statistical qualification by proportional count, coincidence and spectral measurement techniques. Increased measurement times place additional burdens on the baggage handling, cargo inspection, hydrocarbon characterization, process control and geologic operations previously suggested.
The measurement duration may be reduced where additional information is available in the response emissions emerging from the sample location. Intentional, controlled heating of the sample location will induce Doppler broadening of the reaction cross sections and response emission energy spectra. The magnitudes of the changes to the intensities and widths of the characteristic peaks in the response emission energy spectra with known temperature changes provide the additional information about material inventory and composition. If controlled temperatures changes can be induced on time scales that are shorter than the requisite standard proportional or coincidence counting times for the desired accuracy in an isothermal measurement, it is possible to maintain desired accuracy with a comparatively shorter duration count and smaller response emission sample size by observing the magnitude of the Doppler effect on characteristic reaction or emission characteristics in the response spectrum.
The present invention describes a method and apparatus that manifests a controlled temperature perturbation to the sample location concurrently with sample interrogation by ionizing radiation and with detection of the response emission energy spectra. This configuration induces and detects Doppler effects manifested at the sample location, allowing additional measures of material inventory and composition, and allowing a reduction in the requisite counting time or exposure duration. The method and apparatus is intended primarily for the detection of isotopes of Cesium, Iodine, Neptunium, Plutonium, Technetium, and Uranium. Though the magnitudes of the measured effects are substance specific, the contributing physical processes are not strictly material dependent, and the applicability of the method and apparatus is not restricted to the foregoing list of materials, but can be applied to almost any high-energy photon-emitting material.